I remember seeing the old Interlocking Towers with the old style levers that you had to pull on. Exactly how did they work? Was there a cable or rod going to the switch or something? What if was a switch that was down the track or something. I have always been interested on exactly how throwing a lever back and forth switched a track in the old days.
Mike,
Yes, quite fascinating structures. ITs used cables and linkage to “mechanically” foolproof the switching in the tower so that the operators couldn’t inadvertantly direct a locomotive onto the wrong track.
Jim Darnaby has a great article on Interlocking towers in the recent MR issue of How To Build Realistic Layouts (Aug. 2006), on pgs. 58-65. Some of the info is taken from an earlier 2003 or 2004 MR article by the author, unfortunately, of which I can’t find the issue to at the moment. Jim shows in detail how he made one for his layout.
Tom
Tom,
I see, were the cables or rods buried? Wouldn’t it be hard to pull a lever 2 stories up and actually move a switch across the yard. Was there any hydraulics involved? Or something to make the pull easier.
On the New Haven, the Interlocking Machines were located in Signal Stations, or Signal Towers.
The levers cotrolled both the switches, crossings, etc., but also the signals. They were called interlocking machines because they were mechanically designed to prevent lining up a prohibited transit and/or conflicting signal. In other words, a proceed signal could not be indicated until the route was properly lined up.
I am currenty constructing a module of the New Haven’s Old Saybrook (CT) station area including the Signal Tower across from the station. This controlled the access to the five separate tracks through that area including two wye tracks to the Valley line.
The levers were on the second floor along with the track board, an illuminated diagram of the track arrangement under the towerman’s control.
Each lever pulled (or pushed) a vertical rod that ended in a vertical bell crank on the first floor. That bell crank transmitted the motion to another horizontal bell crank exterior to the building along the nearest track. The bell cranks were usually mounted on a concrete block.
Rods (usually threaded together pipe) on rollers connected the the motion to another horizontal bell crank by the switch throw bar and allowed the switch to be opened or closed. In northern climes, these parallel rows of piping were usually covered with with a low wood shed to protect them from snow and icing conditions.
There was no way that a switch could be thrown “down the track” because of this arangement.
In the early days of railroading, in the UK and USA there were too many accidents due to trains runnning afoul of open switches and each other which prompted the railroads to devise signalling and interlocking to enhance safety.
In a pure mechanical interlocking, the machine (which may or may not be in a traditional tower) is connected to the switch points by steel rods. That’s what looks like a layer of pipes parallel to the track in photos of steam-era interlocking plants. Depending on country and era, signals (almost always semaphores) could have been connected by thinner rods or by cables, also routed above the ground.
Inside the machine were two sets of bars, at right angles to each other. One set was connected to, and moved by, the levers. The bars of the other set could only slide if they were not locked by a lever bar, and prevented the operator from either setting up opposing routings or clearing more than one signal. Clearing any signal locked every point lever involved in that route and any opposing route.
I personally saw cable-connected semaphores and mechanically interlocked switches in use on some secondary lines in Japan into the late '60’s, coexisting with ABS, electrical interlocking and CTC on more heavily traveled routes. The signals used a rather elaborate mechanism at the base of the mast to convert horizontal single cable movement into vertical rod movement. In deep snow country, the cable-to-rod device could be well off the ground (and, hopefully, above the drifts.)
Chuck (modeling Central Japan in September 1964 - with electrical interlocking pretending to be manual interlocking)
Nope, they were called “Armstrong” levers for a reason. In later years air, hydraulics, or electricals took on the tasks of moving the points, along with the appropriate interlocking logic. The cables and/or rods were sometimes enclosed in “pipes”, sometimes above ground, other times buried. Needless to say, the aboveground versions were much easier on maintenance.
I beg to differ about actuating switches farther down the yard. Often, older towers, either in early hump yards, or in older flat yards, there were all the Armstrong levers in the tower for (possibly) dozens of switches, some of which may be hundreds of feet away from the tower. Mechanical linkages in the tower would either push or pull the appropriate rod, which would in turn move the bellcrank at the corresponding switch, thus moving the points. In theory, I see no reason you couldn’t activate a switch from over a mile away this way (theoretically speaking).
Brad